Adrenergic Receptor Pharmacology

Key points

• • The adrenergic (sympathetic) system acts through receptors named alpha and beta, which adrenaline and noradrenaline normally activate.
• • Alpha-1 receptors on blood vessels cause them to narrow, so an alpha-1 blocker relaxes the vessels and lowers blood pressure.
• • Beta-1 receptors on the heart speed it up and strengthen its beat, so a beta-blocker slows the heart and reduces its work.
• • Beta-2 receptors on the airways open them up, so a beta-2 agonist relaxes the airways and relieves the tightening of asthma.
• • Because beta-blockers can also act on beta-2 receptors, non-selective ones can tighten the airways, which matters in asthma.
• • Drugs are described as agonists (which switch a receptor on) or antagonists (which switch it off), and as selective if they prefer one receptor subtype.